Caloric vestibular stimulation has long been known as a diagnostic procedure for testing the function of the vestibular system. In the traditional hospital setting, water caloric tests are still used to assess levels of consciousness during acute or chronic brain injury. The brain injury may be due to head trauma or a central nervous system event such as a stroke. Other brain injuries occur in the presence of metabolic abnormalities (e.g., kidney disease, diabetes), seizures, or toxic levels of controlled substances or alcohol. Common techniques to determine consciousness involve simple irrigation of the ear canal with heated (or chilled) water or air. The typical setting for these measures is the hospital emergency room, but water caloric tests are also used in intensive care units and in treating patients admitted to medical or surgical floors. Cold irrigation has also been used in studies testing stroke victims' temporary recovery of cognitive impairments. See Schiff and Pulver, “Does Vestibular Stimulation Activate Thalamocortical Mechanisms that Reintegrate Impaired Cortical Regions?” Proceedings of the Royal Society of London (B) 266: 421-423 (1999).
To reduce the inconvenience of cleaning spilled irrigation fluid, “closed flow” apparatuses, in which an inflatable balloon was configured to be inserted into the ear canal and contain the irrigation fluid, were developed. See, e.g., U.S. Pat. No. 4,190,033 to Foti and U.S. Pat. No. 4,244,377 to Grams. Another more recent development includes electrical stimulation to the vestibular labyrinth by galvanic current applied to the mastoid region. In one study, the current was applied to one or both sides of the head either independently or simultaneously. Ocular monitoring showed levels of brain activity based on eye movement associated with vestibular stimulation. See, Schlosser, et al., “Using Video-Oculography for Galvanic Evoked Vestibulo-Ocular Monitoring in Comatose Patients,” Journal of Neuroscience Methods 145:127-131 (2005).
More recently, caloric vestibular stimulation has been applied to other purposes. O. Kolev, “How caloric vestibular irritation influences migraine attacks,” Cephalalgia 10, 167-9 (1990) describes the relief of migraine symptoms by cold caloric vestibular stimulation.
D. Bachtold et al., “Spatial- and verbal-memory improvement by cold-water caloric stimulation in healthy subjects,” Exp Brain Res 136: 128-132 (2001) (published online 16 Nov. 2000), describe the results noted in the title. In their final paragraph they state “activation arising from vestibular stimulation of the contralesional ear may transiently improve neglected patients' symptoms,” and that their findings indicate “caloric stimulation may improve lateralized cognitive functions whether they are spatial in nature or not.”
U.S. Pat. No. 6,748,275 to Lattner, “Vestibular Stimulation System and Method” describes an apparatus that can be used to “augment or control a patient's respiratory function . . . induce sleep, and/or counteract vertigo.” (column 3, lines 55-60). The apparatus can be invasive or noninvasive (column 7, lines 45-50), and the stimulation can be completed by one or more of electrical, mechanical, magnetic, or thermal stimulation (column 7, lines 50-55). The thermal stimulation can be heated or chilled liquid (column 8, line 65).
US Patent Application Publication No. 2003/0195588 to Fischell et al., “External ear canal interface for the treatment of neurological disorders,” also describes a system for treating neurological disorders. Disorders suggested for treatment include dizziness, vertigo, seasickness and travel sickness (jet lag) (paragraph 17), as well as seizure (paragraph 11).
Y. Yamamoto et al., “Noisy vestibular stimulation improves autonomic and motor responsiveness in central neurodegenerative disorders,” Ann Neurol. 58: 175-181 (2005), state that “noisy GVS (galvanic vestibular stimulation) is effective in boosting the neuro-degenerative brains of patients with multi system atrophy or Parkinson's disease, or both, including those unresponsive to standard levodopa therapy . . . ” (abstract).
V. Ramachandran et al. “Rapid Relief of Thalamic Pain Syndrome Induced by Vestibular Caloric Stimulation,” Neurocase, iFirst, 1-4 (2007), describes the use of caloric vestibular stimulation in the treatment of pain.
A general review of the various uses of caloric vestibular stimulation is given in S. Miller and T. Ngo, “Studies of caloric vestibular stimulation: implications for the cognitive neurosciences, the clinical neurosciences and neurophilosophy,” Acta Neuropsychiatrica 19: 183-203 (2007).
The ear canal is sensitive to foreign objects (U.S. Pat. No. 4,244,377 to Grams at column 2 line 28). Completely-in-the-canal (“CIC”) hearing aids sometimes resolve this problem by producing the hearing aids as soft, resilient, individually cast devices (see, e.g., U.S. Pat. No. 6,249,587 to Clavadetscher et al.), but individual casting of a device can be slow, complicated, and costly. Hence, there is a need for new devices that are useful for delivering vestibular stimulation and other therapies via the ear canal in a manner that is both comfortable and convenient for the wearer.
It is also significant that engaging the ear canal and the inner ear via an insert makes possible numerous therapies and diagnostic techniques directed to the brain. Previous studies have highlighted the therapeutic effects of inducing changes in brain chemistry and blood chemistry by stimulating particular regions of an individual's brain tissue. For example, the suprachiasmatic nucleus (the “SCN”) area of the brain (within the hypothalamus) controls an individual's circadian cycle, keeping multiple body rhythms on a synchronized 24-hour clock (e.g., the sleep-wake cycle, temperature fluctuations, endocrine activity, and metabolic activity). See, Turek et al., “Current Understanding of the Circadian Clock and the Clinical Implications for Neurological Disorders,” Archives of Neurology; 58: 1781-1787 (2001). This “core clock” controls “electrical firing” and “gene expression” that dominate the most basic cellular activities in the body. See, Hastings, et al., “A Clockwork Web: Circadian Timing in Brain and Periphery, in Health and Disease,” Nature Reviews-Neuroscience 4: 649-661 (2003). As might be expected, monitoring an individual's circadian cycles is useful in diagnosing and treating many conditions. See Turek, et al., supra; see also, International Patent Application No. PCT/US2007/020425 (Zhang et al. 2008) (requiring an implanted device for physiological monitoring).
Along these lines, Fuller, et al. note that “neuronal circuits responsible for circadian rhythm genesis, thermal control, feeding, and autonomic function are located in the hypothalamus,” and studies have shown that the hypothalamus is influenced by the vestibular nuclei. “Neurovestibular Modulation of Circadian and Homeostatic Regulation: Vestibulohypothalamic Connection?” Proceedings of the National Academy of Sciences 99:24 15723-15728. See also, Fuller and Fuller, “Genetic Evidence for a Neurovestibular Influence on the Mammalian Circadian Pacemaker,” Journal of Biological Rhythms 21:177-184 (2006). With the body's master clock located within the SCN region of the hypothalamus, there exists a need for controlled monitoring and stimulation of the vestibular system for managing the circadian cycle of an individual in a therapeutic environment. A continued need also exists for a device directed to stimulating the SCN brain tissue and modulating the circadian clock. At least one study has suggested that light therapy could be helpful in this regard. U.S. Pat. No. 6,135,117 (Campbell et al. 2000).
Other regions of the brain also show a potential benefit from a device and associated method for controlled vestibular stimulation. Researchers have determined that the vestibular system provides a direct conduit to the fastigial nucleus, an area of the brain rich with possibilities for assisting in the prevention of cellular ischemia and excitotoxic brain injuries. See Zhou, et al., “Electrical Stimulation of Cerebellar Fastigial Nucleus Protects Rat Brain, in vitro, From Staurosporine-Induced Apoptosis,” Journal of Neurochemistry 79(2): 328-338 (2001); Siebold, et al. “Fastigial Nucleus Activity During Different Frequencies and Orientations of Vertical Vestibular Stimulation in the Monkey” Journal of Neurophysiology 82: 34-41 (1999). Ongoing research has also determined that the vestibular system is connected to the brain's release of acetylcholine from the hippocampus. Horii, et al., “Effects of Vestibular Stimulation on Acetylcholine Release from Rat Hippocampus: An In Vivo Microdialysis Study,” Journal of Neurophysiology 72:2 605-611 (1994). Similar results have shown the increased production of histamines via vestibular stimulation of the hypothalamus. Horii, et al., “Effect of Unilateral Vestibular Stimulation on Histamine Release from the Hypothalamus of Rats In Vivo,” Journal of Neurophysiology 70:5 1822-1826 (1993).
Vestibular stimulation has also been linked to blood chemistry changes that can be of use in treating various disease states. First, an increased concentration of ascorbic acid in the human body has been shown to result from cold water vestibular stimulation. See, Zhang, et al., “Change of Extracellular Ascorbic Acid in the Brain Cortex Following Ice Water Vestibular Stimulation: An On-line Electrochemical Detection Coupled with In-vivo Microdialysis Sampling,” Chinese Medical Journal 121:12:1120-1125 (2008). Research also suggests that the inner ear is a logical place to stimulate heat shock protein formation for protection against acoustic over-exposure. Sugahara, et al., “Heat Shock Transcription Factor HSF1 is Required for Survival of Sensory Hair Cells Acoustic Overexposure,” Hearing Research 182: 88-96 (2003). Vestibular stimulation is one way to induce the heat shock protein response.
Yet another area of development involves the association between vestibular stimulation and the insula region of an individual's brain, which is critical in an individual's sensory system (particularly auditory), motor association, and vestibular activity. Bamiou et al., “The insula (Island of Reil) and its role in Auditory Processing,” Brain Research Reviews 42:143-154 (2003). The insula is particularly reactive to thermal stimulation. See, Craig et al., “Thermosensory Activation of Insular Cortex,” Nature Neuroscience 3:2: 184-190 (2000). The insula, therefore, is a prime area for researching the effects of caloric vestibular stimulation. This is particularly true for research and therapies that use holistic approaches to wellness, including meditation as a means for achieving clinical results in physiology and psychology. Research has shown a correlation between successful meditation and insular activity. Lutz et al., “Regulation of the Neural Circuitry of Emotion by Compassion Meditation: Effects of Meditative Expertise,” Public Library of Science—PLoS One 3:3:1-10 (2008). Given the insular response noted upon the exposure of a body to thermal stimulus, the insula has significant potential in the area of hot flash management and other rapid changes in body temperature.
Accordingly, developments in stimulating the vestibular system of an individual are potentially beneficial to take full advantage of physiological responses that are useful in treating and diagnosing a variety of medical conditions. These conditions include but are not limited to Alzheimer's Disease, diabetes, obesity, heart disease, epilepsy, vertigo, hypercusis, fibromyalgia, menopause, phantom limb pain, migraine and numerous conditions for which the prescribed medicines work optimally at a particular point in a circadian cycle.